Motor fuels are used in a variety of systems. In the broadest sense, a motor fuel is one which is used in piston or turbine engines. The present invention is directed to fuels for a variety of spark-ignited combustion engines including higher rpm engines as well as piston engine useful in ground vehicles and/or certain aircraft engines and/or unmanned aviation vehicles (UAV). Typically, ground vehicles can use relatively lower octane fuels, while aircraft require higher octane fuels. A basic determinant as to the choice of fuels is the octane rating of the fuel compared to the compression of the engine. For example, higher compression engines generally require higher octane fuels. Another determinant is the fuel's burn speed in the combustion chamber. Higher rpm engines tend to favor faster burning fuels in a controlled combustion process (i.e. without exploding) to prevent engine knocking. So, many engine designs have evolved calling for specialized fuels tailored to unique needs balancing engine performance between higher octane vs. faster burn speed.
A particular aspect of the present invention is to provide formulations which are useful as piston engine fuels, and are particularly suited for use in automobiles, high rpm auto racing engines as well as aviation gasoline applications. Aviation gasoline has a number of special requirements as compared to ground vehicle gasoline. Aviation gasoline (called “avgas”) is an aviation fuel used in spark-ignited (reciprocating) piston engines to propel aircraft. Avgas is distinguished from mogas (motor gasoline), which is the everyday gasoline used in motor vehicles and some light aircraft. Most grades of avgas have historically contained tetraethyl lead (TEL), a toxic substance used to prevent engine knocking (detonation).
This invention produces an unleaded grade of gasoline with fuel properties that meet the minimum power rating (motor octane number), appropriate combustion anti-knocking (detonation suppression), volatility (vapor pressure), and related criteria for piston engine aircraft and thereby complies with all current requirements of ASTM 4814, ASTM D910 and ASTM D7547 fuel. The inventive fuels allow a range of automobiles and piston engine aircraft, including those with higher rpm and high-compression engines, to perform effectively to manufacturer requirements.
Aviation gasoline must meet the power demands for aircraft engines. The motor octane number, or MON, is a standard measure of the performance of an aviation fuel. The higher the MON, the more compression the fuel can withstand before detonating. In broad terms, fuels with a higher motor octane rating are most useful in high-compression engines that generally have higher performance.
The MON is a measure of how the fuel behaves when under load (stress). ASTM test method 2700 describes MON testing using a test engine with a preheated fuel mixture, 900 rpm engine speed, and variable ignition timing to stress the fuel's knock resistance. The MON of the aviation gasoline fuel can be used as a guide to the amount of knock-limiting power that may be obtained in a full-scale engine under take-off, climb and cruise conditions.
Another particular issue with avgas is its ability to start reliably under a wide range of altitude and climate conditions. Avgas needs to have a lower and more uniform vapor pressure than automotive gasoline so it remains in the liquid state despite the reduced atmospheric pressure at high altitude, thus preventing vapor lock. The ability of an aviation gasoline to satisfy this requirement may be assessed based on the Reid Vapor Pressure (RVP). A typical requirement for avgas is that it have an RVP of 38-49 kPa at 37.8° C., as determined in accordance with ASTM D5191.
Avgas must also be highly insoluble in water. Water dissolved in aviation fuels can cause serious problems, particularly at altitude. As the temperature lowers, the dissolved water becomes free water. This then poses a problem if ice crystals form, clogging filters and other small orifices, which can result in engine failure. Accordingly, alcohol components are generally not used in aviation fuels due to their tendency to be water soluble.
In light of this background, there remains a need for additional and/or improved fuel compositions.